In U.S. Pat. No. 3,105,395, issued Oct. 1, 1963, assigned to the same assignee as the present invention, there has been set forth a highly effective and commercially successful system for obtaining the recognized advantages of a multicountershaft transmission while maintaining in a very simple manner the equality of torque transmission through the said countershafts. The transmission set forth in this patent provides both an input shaft and the countershafts on fixed axes with the gears thereof being immovable radially with respect to the respective shafts on which they are mounted. The output shaft, however, or main shaft, is floatingly mounted for movement transverse to a plane through the axes of two countershafts and the main shaft gears when the main shaft gears are unclutched from the main shaft. The main shaft gears, which are supported on and by the countershaft gears, encircle the main shaft with sufficient clearance to permit movement of the main shaft radially with respect to the gears. Thus, the main shaft can move radially with respect to the gears to which it is not clutched but the gear to which said main shaft is clutched and said main shaft are radially movable as a single unit transversely with respect to the plane connecting the axes of the two countershafts in order to equalize the torque received onto the main shaft from each of such countershafts. The movement accurately follow irregularities in the gears and their mounting means whereby the system works well and has received wide commercial acceptance.
In U.S. Pat. No. 3,237,472, issued Mar. 1, 1966, also assigned to the same assignee as the present application, there is disclosed the utilization of a floating main shaft having improved shaft mounting means together with an output shaft on a fixed axis. This patent was for certain purposes an improvement over the earlier U.S. Pat. No. 3,105,395 but was not fully satisfactory in that the specific means shown in the earlier patent for supporting the main shaft and/or connecting same to power transmitting means are relatively expensive to manufacture, somewhat awkward in assembly and utilized an appreciable amount of longitudinal space.
In U.S. Pat. No. 3,335,616, issued Aug. 15, 1967, also assigned to the same assignee as the present application, there is disclosed the utilization of a fixed main shaft rotatably supported at both ends by bearings. Furthermore, the transmission set forth in this patent provides also for an input shaft and the countershafts being supported on fixed axes with the gears thereof being immovable radially with respect to the respective shafts on which they are mounted. The main shaft gears are also here supported on and by the countershaft gears and, when unclutched from the main shaft, said main shaft gears encircle the main shaft with sufficient clearance to permit movement of the gears radially with respect to the main shaft. Thus, the unclutched main shaft gears can move radially with respect to the main shaft but the gear to which the main shaft is clutched is rotatable as a single unit therewith. In this embodiment, however, the means for clutching the gear to the main shaft is floatingly mounted for movement transverse to the main shaft in a plane connecting the axes of two countershafts so that the gear clutched to the main shaft by the floating clutch means will continue to be floatingly oriented with respect to the main shaft in order to equalize the torque received onto the main shaft from each of such countershafts. This system also works well and has received good commercial acceptance.
It is to be noted that in the three above-mentioned patents, the main shaft is supported in a centered position between two countershafts. In U.S. Pat. Nos. 3,105,395 and 3,237,472, both ends of the main shaft are permitted to float in directions transverse to the plane passing through the axes of two countershafts. The specific means shown in these patents for supporting the main shaft are effective but are relatively expensive to manufacture.
The device shown in U.S. Pat. No. 3,335,616, which utilizes a main shaft supported for rotation about a fixed axis, is also effective but relatively expensive to manufacture due to the provision of floating clutch means on the main shaft. Particularly, the floating clutch means are expensive to manufacture because they must maintain a tolerance which will permit them to float on the main shaft while at the same time which will not result in a sloppy coupling between the main shaft gear and the main shaft.
In U.S. Pat. No. 3,500,695, issued Mar. 17, 1970, also assigned to the same assignee as the present application, there is disclosed the utilization of a mainshaft having one end floating and the other end pivoted. The transmission illustrated in this patent was for certain purposes an improvement over the transmissions illustrated in earlier patents, but was not fully satisfactory as the main shaft was, in certain conditions, subject to axial thrust loads tending to cause undesirable axial shifting of the main shaft and unequal and/or excessive wear on certain transmission components such as the clutch teeth or the like.